This invention relates to stiction reduction in a magnetic disc drive, and particularly to the use of microvibration in an actuator arm of a disc drive to reduce stiction.
In magnetic disc drives, the transducing head is ordinarily carried on a slider having an air bearing surface that permits the slider to "fly" a small distance over the disc surface. The slider, which is supported by a gimbal spring, which in turn is attached to an actuator arm, is permitted to "land" on the disc surface when the disc drive is inactive. Hence, when the disc is not rotating, the slider "lands" on the surface, usually at a landing or parking zone dedicated to that purpose. When the disc drive is rotated at its operational velocity, the spinning disc creates windage, causing the slider to "fly" a small distance above the disc surface. The air bearing surface of the slider and the surface of the disc are ultra smooth, enabling the slider to fly the transducing head only a few microinches or less above the disc surface.
However, a problem arises when the slider has landed on the disc. Stiction between the ultra smooth disc surface and ultra smooth air bearing surface of the slider inhibits the startup of rotation of the disc, requiring a significant amount of torque in the disc spindle motor to overcome. Stiction is the result of the adherence of the slider to the disc and is aggravated by the adhering qualities of lubricants and contaminants on the disc surface causing the slider to "stick" to the disc surface. Numerous techniques are employed in disc drives to reduce the problem of stiction. For example, it is common to provide the landing or parking zone of the disc surface with a textured or rough surface to admit air under the slider so that the air bearing surface of the slider is not in full contact with the disc surface. Another technique is to operate the voice coil motor associated with the actuator arm to move the slider radially with respect to the landing zone on the disc simultaneously with operation of the spindle motor to rotate the disc relative to the slider.
There is a need to increase data capacity on discs by increasing the density of data recorded along a track of a disc and by decreasing the spacing of concentric tracks to thereby increase the number of tracks on the disc. The increase in data capacity results in the need for even smoother discs and air bearing sliders to permit the head to fly even closer to the disc surface, as well as increased precision of the speed of the motors driving the disc spindle and the actuator arm. However, increased smoothness presents the risk of increasing stiction, and increased speed precision of the motors can only be accomplished at a sacrifice of torque, which is needed to overcome stiction. Hence, a need exists to overcome the effects of stiction without sacrificing smoothness of the disc and air bearing surfaces and without sacrificing speed precision requirements of the motors. As a result, if stiction can be overcome, the spindle motor may be designed for speed, rather than torque.